Looking at bottom right of radiator.
05 R53 JCW 153K miles. Losing half a gallon of coolant every 150 miles. Not good at all.

 

I’d say that radiator is toast. I high recommend that you stop driving until this problem is fixed. These cars have a low bs threshold for being run low on coolant. That temp gauge in the dash is a bs gauge and it already might be running hot.

 

That's what I was afraid of, but it's nice to get verification. I wish I could stop driving but it's my daily driver.

What is the deal with the temp gauge? I've seen several comments that it's not really a gauge and I've noticed it doesn't respond like a normal gauge.

 

Is aftermarket gauge a "must-have"???

 

The temp gauge movements are “filtered” for lack of a better word.

I suggest you stop driving it unless you can afford a head gasket.

 

Ended up being the radiator. Also had to replace the radiator support. The crack caused it to move around which probably contributed to the leak.

 

The gauge operates linearly up to 75C, when it reaches the halfway point.
It stays exactly there from 75C to 125C, and starts to climb again above 125C.

 

Thanks for that info cristo.
Any way to convert it to a "normal" gauge? From what I understand the signal goes through the ECU.